Posted on 10/26/2020 10:27:51 PM PDT by LibWhacker
NFN, but if it wasn’t a Holiday Inn Express, it doesn’t count.
This is exactly how long it takes for Schumer to step in front of a camera or Pelosi to eat a pint of ice cream.
This distance is the speed of light going about 74 picometers, just over half the above-stated size of the hydrogen atom, 120 picometers. (247 10^-21 s x 3 10^8 m/s = 74.1 10^-12 m)
No, it’s a hydrogen molecule. Free hydrogen
atoms don’t exist (at least under any conditions likely to be encountered on earth, with the possible exception of a hydrogen bomb explosion or a hypothetical fusion reactor). Hydrogen molecules are two hydrogen atoms covalently bonded to form one hydrogen molecule. On earth, hydrogen molecules generally don’t occur naturally. Most hydrogen atoms are bound to oxygen to form water. (Some are bound to carbon, nitrogen, sulfur and phosphorus atoms in various organic compounds). Hydrogen gas is formed chemically via reaction of certain metals with water, or more commonly by electrolysis. The freed hydrogen atoms quickly bond in pairs and we never observe free atoms, but diatomic molecules of hydrogen.
Ah, got it; since it is knocking out two electrons, the distance the light travels is the distance between them.
Nice.
Thanks for sharing! :)
That’s a good thought, but you don’t quite run into the uncertainty limit here (but it’s close). Usually the uncertainty relation is expressed in terms of position and momentum, but it can be equivalently expressed in terms of energy and time uncertainties, a more useful form for this experiment. The relation is the same — the product of the uncertainties cannot exceed Planck’s constant.
The time uncertainty cannot exceed the claimed measured value, which is on the order of 10^-19 seconds. Planck’s constant is on the order of 10^-34 Js. Therefore the energy uncertainty is limited to being at least 10^-15 J. This uncertainty is at least equal to the energy of the incoming x ray photon; at any given time the energy could be or could not be increased by this amount. Depending on the frequency used, this energy could be right around 10^-14 to 10^-15 J, so it’s close, but it doesn’t run afoul of Heisenberg (obviously, or the refutation of quantum mechanics would be the big story, not the measurement of a record short time).
Not really. H2O naturally dissociates into hydroxide and hydronium ions. The hydronium ion is formed when the oxygen from one water molecule “steals” a hydrogen atom from another, thus giving an ion with the formula H3O+. For simplicity, the hydronium ion is often suppressed in chemical equations and it’s unhydrated equivalent, the hydrogen ion H+ used instead. Even that, though is not a hydrogen atom. A hydrogen atom is a proton plus an electron. The hydrogen ion is a just a proton.
BTW this dissociation of water is a very weak reaction; almost all the water remains undissociated.
Hmmm... Soon we’ll be able to measure the mental-thought retention span for joe biden, knees harris, and AOC...
See my post 48. The measurement of the distance between two electrons is still a distance measurement, and thus subject to the uncertainty relation. You can’t get around it by changing by your reference frame. What you are describing is determining the position of electron B using electron A as an origin. It’s still a measurement of position. The experiment as described does not circumvent the uncertainty relation since that isn’t possible. It also does not violate it, which should be no surprise since the measurement of a record short time interval, while impressive, would not be anywhere near the significance of overturning quantum mechanics. That would certainly be Nobel Prize worthy.
Isn’t it the equal number of H+ and OH- that results in a neutral pH for pure water?
Isn't that a theoretical value - i.e., a value arrived at, not through direct observation, but rather "only" mathematical calculations?
Didn't some physicist simply "prove," on the chalkboard, that the half-life is 10^-20 seconds? Or perhaps it was inferred?
That is different than observing it.
Regards,
pH is the negative logarithm of the hydrogen ion concentration. Dissociation of water happens to produce a concentration of almost exactly 10^-7 M. Hence the pH of pure water is 7. We call this neutral since it’s pure water without any acid or base added. So yes, dissociation of water gives the pH value of a neutral solution, but the actual value of that pH is experimental. In fact, it’s not true that pH 7 is always neutral. For example, a biochemist would tell you that a sample of a body fluid with pH 7 is slightly alkaline. That’s because the extent of dissociation is temperature dependent. At body temperature, it occurs a bit more, giving a slightly higher concentration of H+, with 6.8 (IIRC) being neutral.
That’s absolutely right. The decay of a radioactive nucleon is described by an exponential decay law. That is if A is the amount left at any given time, and B is the amount present at some initial time, then these are related by A = B * exp (-kt), where t is the time that passed since the initial time and k is a (positive) constant. Plotting the natural logarithm of the amount remains vs. time give a straight line with slope equal to k, allowing it to be determined easily. Setting A = 1/2 B in the decay law once k is determined allows easy determination of the half life without the need to measure an actual time as short as the half life; longer times will suffice assuming enough material to start with plus sufficiently sensitive detection procedures.
So, THAT'S how those Photon Torpedoes work...always wondered about that!
Gosh, I’m not a chemist.
Yes, yes, but, in the case of an isotope like He-5 (with a half-life of 10^-20 seconds when decaying to He-4), it is not practically possible to actually observe decays. I am therefore assuming that this figure (10^-20 seconds) was not arrived at experimentally, or through observation, but rather "on the blackboard" (or, more likely, through inference).
Please feel free to correct me, if you can.
Regards,
It can be done experimentally, but it doesn’t require measurements of time as short as the half life. For the example you provide, it’s possible that it was done via theoretical calculation; I don’t really know for sure. My point was that it’s not necessary to use the half life as your time unit. Times between measurement of amounts of material can be significantly longer than the half life. For instance 50 half lives would result in a reduction by about 10^-15. With a good mass spectrometer and a large enough sample, this would be detectable. This would also allow experimental determination of half life.
This isn’t really my field, so this is only speculation, but it may also be possible to determine half lives of very unstable nuclides by taking advantage of special relativity. The half life is a proper time, which means a time measured by an observer in a comoving reference frame with the include. If a nuclide is accelerated to near light speed, it could theoretically be made to last quite a bit longer as measured by a laboratory clock. Particle accelerators are quite capable of accelerating a beam of He5 nuclei to such high speeds. There is no theoretical limit on the time dilation factor that can be achieved. A time dilation factor of even 10^6 or so would make the experimental measurement of the half life possible.
I have no dispute with you - but most of your remarks up till now, while scientifically sound, would be totally impractical for measuring the half-life of a substance as short as that of He-5.
With regards to your latest remarks - that one could observe the substance for a period of time many factors longer than its (short) half-life: That presupposes that one has a sufficient quantity of the substance in question - but the shorter the half-life of a substance, the more radioactive it is, and the more energy per unit of time it releases.
In the case of a substance with such an extremely short half-life as He-5, any amount of the substance that could be scraped together (but how?) even only approaching macroscopic quantities would be so volatile as to preclude experimental observation.
A good comparison would be the case of the determination of the half-lives of super-heavy transuranic elements, with Atomic Numbers of, say, 103 and above. They all have half-lives on the order of mere seconds, if I recall correctly (many isotopes with half-lives of only fractions of a second).
If I understand it correctly, scientists have never been able to produce more than a few atoms at a time of such transuranics - certainly never enough to actually take a measurable quantity and wait for several half-lives to see how much of the original sample has "survived" and thus to determine the half-life using the method you proposed in your last comment above.
Instead, they bombard macroscopic targets of heavy elements (like Uranium) with, say, Xenon nuclei in a cyclotron, and then observe the decay in cloud chambers. Every now and then, they observe the millimeter-long track of a nucleon (travelling at near light-speed - so relativistic effects like the one you mentioned do, indeed, have to be taken into consideration) in the cloud chamber, deduce its mass and charge (the cloud chamber has been placed in an artificial magnetic field), and calculate its lifetime.
My point is that no physicist has ever had anything like a macroscopic sample of these transuranides, and has never been able to, say, weigh it and then wait and watch (over multiple half-lives) as it diminishes in mass.
But this really isn't my field either, so feel free to correct me!
Regards,
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